Pro-inflammatory Th1 and Th17 T-lymphocytes orchestrate many organ-specific autoimmune diseases, such as multiple sclerosis (MS) and type I diabetes. The pathologic activity of these cells can be modulated by different forms of regulatory T lymphocytes (Treg), most prominently Treg expressing the Foxp3 transcription factor. Adoptive immunotherapy with Foxp3+ Treg therefore holds promise in the selective treatment of autoimmune conditions. Our laboratory has specifically focused on the therapeutic application of Foxp3+ Treg that are generated by conditioning naove T lymphocytes with TGF-2. We demonstrated that the cellular properties of these induced Treg (iTreg) differ from those of directly isolated endogenous Treg (natural Treg, nTreg). Despite this, iTreg and nTreg are equivalently potent in treating a model autoimmune disease, experimental allergic encephalomyelitis (EAE), and operate through similar mechanisms. In this proposal, we will address the unique biology of iTreg, and lay a foundation for their clinical translation into a cellular immunotherapeutic. In preliminary studies we demonstrated that a large proportion of iTreg, but not nTreg, lose Foxp3 expression after adoptive transfer. One key difference between iTreg and nTreg is in their extent of self-specificity. Self-specificity will impact T-cell homeostasis, and we hypothesize will also influence iTreg survival and function. In Aim 1, we will study the role of TCR specificity in iTreg survival, Foxp3 preservation, and therapeutic activity. Our preliminary data shows that iTreg, like nTreg, are highly potent, operate to prevent and treat EAE in an IL-10-dependent manner, and catalyze the development of additional autoantigen-specific Treg (infectious tolerance). In Aim 2, we will determine how iTreg induce immune tolerance by diverting a pathologic immune response into a regulatory response, and the specific role of IL-10 in this. We have further demonstrated that TLR ligands dramatically enhance the preservation of Foxp3 expression in and survival of therapeutically transferred iTreg. We hypothesize that TLR activation, either through APC or directly into iTreg, promotes the survival and activity of iTreg. In Aim 3, we will identify how innate immune pathways alter iTreg therapeutic activity, and probe a possible adjunct role for TLR agonists in iTreg induction and immunotherapy. These studies will provide new insights into how iTreg modulate immunity after therapeutic transfer and how they may be functionally optimized to maximum potency and efficacy, and will facilitate the clinical translation of iTreg immunotherapy